1. Field of the Invention
The present invention relates in general to a shielded flat cable used for signal transmission in wiring electronic appliances. More specifically, the invention relates to improving the electrical connection between a grounding conductor and a shielding layer of a flat cable to provide a consistent low resistance between the grounding conductor and shielding layer to improve shielding.
2. Description of the Related Art
Flat cables are becoming increasingly popular for use as interface transmission wires. More and more, flat cables are replacing the twisted wires and coaxial lines. Flat cables are, however, more highly susceptible to externally induced noise and interference than both twisted wires and coaxial lines. Therefore, flat cables generally have built in shielding layers.
A shielding layer is ineffective unless properly grounded. Grounding the shielding layer in a flat cable is typically accomplished by connecting it to a ground wire conductor built in the cable. The quality of shielding is directly related to the quality of the ground connection.
FIG. 1 (PRIOR ART) and FIG. 2 (PRIOR ART) are cross-sections of two connection arrangements used in standard flat cables. As shown in FIG. 1 (PRIOR ART), two flat conductors are stacked on each other to form a ground wire 2. One of the flat conductors is bent so as to be in physical contact with a shielding layer 1. Physical contact between the ground wire and shielding layer provides the electrical connection. FIG. 2 (PRIOR ART), is a schematic cross section of a second electrical connection arrangement of another typical flat cable. Ground wire 2 and transmission wires 3 are covered on their outside surfaces with an insulating material 4. The insulating material 4 is removed above the ground wire and replaced with a conductive adhesive agent 6. The adhesive agent 6 electrically connects the ground wire 2 to the shielding layer 1.
In the above-discussed flat cable arrangements, the resistance between the shielding layer and the ground wire is relatively high and variable; thus, the shielding effect is relatively poor and also variable. For example, in the shielded flat cable shown in FIG. 1, resistance between shielding layer and ground varies from 50 m.OMEGA. to 200 m.OMEGA..